I. Field of the Invention
The present invention relates to rotor attachment assemblies, and more particularly relates to such a structure which provides for coaxiality of a rotor and a rotor shaft and which thereby provides against bending of the shaft.
II. Description of the Prior Art
A variety of conventional mechanisms include rotors or the rotating part of a mechanical device. Conventional turbine engines and turbomechanisms such as turbochargers as the primary examples include impellers as rotors which are driven by fluids. According to the prior art, customary practice has been to mount the impeller, which is that member of the rotor class of which we are primarily concerned, on a drive shaft. To rigidly fix the impeller (or rotor) to the drive shaft, a substantially standard nut has conventionally been used. Known drive shafts include a smooth body which terminates at a shoulder leading to the nut-receiving threads defined in the end portion of the shaft.
As is conventionally known, the length of the smooth body is equivalent to the length of the shaft-receiving aperture in the impeller. Accordingly, when the impeller is fully pressed upon the shaft, only the threaded portion of the shaft extends beyond the rotor. The rotor is then secured to the shaft by a conventional nut, possibly in combination with one or more flat or lock washers, which press against the rotor. The nut base (or a washer) and the surface of the rotor mate with one another in this construction.
Known methods of fastening a rotor to a rotor shaft suffer from a variety of disadvantages. First, using conventional retention methods, the shaft may bend in response to non-uniform loading due to improperly manufactured tolerances. These errors, even though relatively slight, nevertheless cause non-parallelism of the assembled rotor and the nut mating surfaces.
A bent rotor shaft results in at least two problems which affect performance. First, the rotor's center of gravity is shifted resulting in rotational imbalance. Second, the rotor embodies increased radial runout, thus reducing or possibly eliminating fin clearance.
In response to these undesirable characteristics, attempts have been made to minimize shaft bending by incorporating spherically-faced nuts and washers or by making manufacturing tolerances more stringent. However, spherically-faced nuts and washers require trial-and-error adjustment. Readjustment is often subsequently required. More stringent manufacturing tolerances result in manufacturing cost increases.
Accordingly, prior inventions have failed to eliminate the problems commonly associated with known rotor assembly designs.